Studies on the effects of chronic marihuana use have been complicated by lack of controlled quality in the material smoked, by uncertainties inherent in long-term studies with an illicit drug in humans, and by the lack of purified constituents of marihuana that might be employed to separate the effects due to these various constituents. Our proposed research has the ultimate objectives of determining long- term (five years) exposure on behavioral and histopathological effects of smoked standardized marihuana, at several levels of exposure, in beagle dogs. Parallel studies would determine the effect of delta-9- tetrahydrocannabinol (THC) smoked in placebo cigarettes, and of this same compound inhaled as an unheated aerosol. We would thus hope to distinguish between the effects of the drug as commonly consumed, the supposed active ingredient, and the effect of combustion. Corollary studies would seek to identify the products formed by metabolism of the materials inhaled in the smoking studies. The more limited objectives of the initial year's effort on this study are the demonstration of the feasibility of employing dogs in a study of this sort (the adapting of equipment and the identification of measurable effects) and the development of a detailed protocol for the long-term studies.